This invention relates to a method and an apparatus for the batch-wise or continuous production of webs, panels or sandwich elements of foam plastics reinforced with rovings and in particular with glass fiber rovings, in which method the rovings are deposited on a support and permeated with a foam produced from a reaction mixture ejected from a nozzle. The apparatus according to the invention for carrying out the process batch-wise comprises a mold, with or without a cover, above which a displaceable mixing head is arranged. The apparatus for carrying out the process continuously comprises a conveyor belt with raised edges to limit its width and optionally a covering belt, and a mixing head which is reciprocally movable transversely to the direction of delivery and which is arranged above the conveyor belt.
It is generally desired that webs or panels of foam plastics or the foam plastic core of sandwich elements which have covering layers on either side of the core be reinforced with fiber inserts. These fiber inserts usually consist of glass fiber mats of fiber fleeces. They generally produce a foam of higher density in the marginal zones of the foam plastic product or of the foam core of a sandwich element. Additionally, if these mats or fleeces cannot be fixed to the internal surfaces of covering layers, they are liable to become displaced when the reaction mixture is introduced or when it foams up. It is not always desired to produce foam products or foam cores which have a higher density in the marginal zones. In such cases it has previously been necessary to introduce chopped rovings into the foaming mixture or to produce fiber mats substantially equal in thickness to the finished webs or panels of foam. In the former case, the chopped rovings are liable to be unevenly distributed when the reaction mixture foams up. In the second case, it is extremely difficult to produce glass fiber mats of the required thickness, for example, 4 cm or more, store them and then work them up as required without the mats suffering any loss in thickness. Even if this were easy to carry out, the mats would still be liable to be deformed by the reaction mixture as it foams up. When the foams are to be reinforced with mats and fiber fleeces, the dense arrangement of the fibers makes it difficult for the foaming mixture to penetrate the gaps between the fibers. This inability of the foam to pass through the gaps between the fibers causes the undesirable displacement of the mats and fleeces.
Due to the difficulties mentioned above, the fiber reinforced foam products or sandwich elements do not have sufficiently long fire resistance. It has been found, however, that the fire resistance can advantageously be increased by avoiding the formation of cracks which is liable to occur in the aforesaid products if they are exposed to heat. The reason for this is that early destruction of the foam begins at these cracks.
It is therefore, an object of this invention to provide means by which webs, panels or sandwich elements of foam plastics reinforced with rovings and in particular with glass fiber rovings can be produced in such a way that they will have a high resistance to the formation of cracks. The important properties which are desired to be achieved are not only a high resistance to mechanical stress in general, but in particular an improved fire resistance.